You select a command, and one of the elements looks like this:
That means you are allowed to put a number or a text string in that cell.
If you want the text to include a space, you must enclose the text between quotes. You must also enclose the text between quotes if you want to include '\' or any control characters within the literal using standard escape sequences (\r, \n, \t, \f, \\, etc).
Once you've replaced the Literal legend, the cell will forever remain the color associated with a Literal as a reminder that this element of the command must be a literal.